1. Field of the Invention
This invention relates to a highly-oriented diamond film wherein grain sizes are oriented in order unlike a polycrystalline diamond film wherein grain sizes are randomly oriented, and more particularly, to a highly oriented diamond film suited to applications as diamond semiconducting sensors, electronic devices, integrated circuits, electronic parts, optical parts and the like.
2. Prior Art References
Diamond is excellent in heat-resistance and heat conductivity, and its band gap is as big as about 5.4 eV. Diamond is an electrical insulator, and its dielectric breakdown voltage is, for instance, approximately more than thirty times as high as that of silicon.
The technique to synthesize diamond film by chemical vapor deposition is well known (Japanese Patent Publications Nos. 59-27754 and 61-3320).
In this method of synthesizing a diamond film, a mirror-like finished silicon substrate is mechanically polished using diamond paste or powder to make scratches thereon, and then placed in a flow of mixed gas of CH.sub.4 +H.sub.2 containing about 1% methane to subject to microwave irradiation in this state to produce plasma around the substrate. By this process, diamond particles are deposited on the substrate to form a polycrystalline diamond film.
It is also known that a p-type semiconductor can be synthesized by doping boron (B) atoms (Japanese under Provisional Publication No. 59-137396). Furthermore, the technique has been disclosed by which electronic devices, such as diodes and transistors excellent in heat-resistance, are manufactured using semiconductor diamond films (K. Miyata, D. L. Dreifus, and K. Kobashi, Applied Physics Letters, Vol. 60, No. 4, p. 480 (1992) and A. J. Tessmer, K. Das and D. L. Dreifus, Diamond and Related Materials, Vol. 1, P. 89 (1992)).
It is also known that a single crystal diamond film can be synthesized by chemical vapor deposition on a single crystal diamond substrate, which is referred to as the homoepitaxial diamond film.
According to the methods described in Japanese Patent Publications Nos. 59-27754 and 61-3320, no other film than what we call a polycrystalline film, wherein diamond crystals are randomly oriented, can be synthesized on a substrate. Such a polycrystalline film presents some problems: the surface roughness of the polycrystalline film is as much as 0.1-0.5 .mu.m: its electrical properties are inferior because of grain boundaries present among diamond crystals which scatter or trap carriers (electrons and holes).
Although a homoepitaxial diamond film formed on a single crystal diamond substrate offers no such problems, a commercially available single crystal diamond has a disadvantage that its area is usually smaller than 5 mm.times.5 mm, which is too small to be employed for the production of electronic and optical parts.